1. Field of the Invention
The present invention relates to a variable flow valve, which is used in breather circuits for fuel tanks.
2. Description of the Related Art
In the vicinity of automobile fuel tanks, a vaporized-fuel circulating system, a so-called evaporator circuit, is disposed. The evaporator circuit leads vaporized fuels from fuel tanks to external canisters. The vaporized fuels are then adsorbed to activated carbon, and are stored temporarily therein. Thus, the evaporator circuit inhibits the vaporized fuels from being emitted into the outside air. The canisters are connected with engines, and engines exert an inlet negative pressure to release the adsorbed vaporized fuels from activated carbon to remix them into an air-fuel mixture. Accordingly, the adsorbed vaporized fuels are reused as fuels.
However, when a fuel sucks in fresh air through a fuel supply opening in a large volume in supplying fuel to an automotive fuel tank, fuel vaporizes facilitatively in the fuel tank. Accordingly, the volume of gases flowing to the canister increases. Consequently, there might arise a problem that the adsorption amount of gases to the canister has increased. Hence, the fuel tank is provided with a breather tube which communicates the gaseous phase in the fuel tank with the outside air. The breather tube is connected with a part of an inlet pipe, part which is positioned adjacent to a fuel supply opposite opening of the inlet pipe, at one of the opposite ends. Moreover, a breather nipple, which is fixed so as to communicate with the gaseous phase in the fuel tank, is fitted into the other opposite end of the breather tube. Therefore, the vaporized fuel present within the fuel tank in supplying fuel passes the breather tube through the breather nipple, and circulates again to the fuel tank by way of the inlet pipe. Thus, the fuel is inhibited from being sucked in fresh air. In addition, it is possible to reduce the adsorption amount of vaporized fuel to the canister, because the fuel is inhibited from vaporizing.
Note that an orifice for controlling a breather gas volume is usually formed in the breather nipple so as not to increase the breather gas volume, which circulates from the breather tube to the inlet pipe, more than an air volume, which is sucked in at the fuel supply opening.
Hereinafter, the circuit of gas circulating from the fuel tank, the breather nipple, the breather tube, the inlet pipe, and again to the fuel tank in this order will be referred to as a “breather circuit.”
Here, the fuel-supply rate in supplying fuel to fuel tanks can be divided into two types, a low rate represented by 15 L/min. and a fast rate represented by 38 L/min., depending on the specification and usage of fuel supply guns. Moreover, it is required to increase the breather gas volume circulating in the breather circuit in fast-rate fuel supply, because fuels suck in air more in the first-rate fuel than in the low-rate fuel supply.
In order to increase the breather gas volume circulating the breather circuit in fast-rate fuel supply, it is effective to enlarge the opening of the orifice. However, when enlarging the opening of the orifice, the breather gas volume circulating the breather circuit has increased even in low-rate fuel supply. Accordingly, the breather gas volume circulating the breather circuit has surpassed the sucked-in air volume in a low-rate fuel-supply range. Consequently, vapor leakage might occur through the fuel supply opening.
On the contrary, when diminishing the opening of the orifice, it is possible to prohibit vapor leakage in low-rate fuel supply. However, when diminishing the opening of the orifice, the volume difference has increased between the sucked-in air volume and the breather gas volume in fast-rate fuel supply. Accordingly, sucked-in fresh air facilitates the vaporization of fuel in the fuel tank. Consequently, the adsorption amount of vaporized fuel to the canister has enlarged. Under such contradicting circumstances, there might arise a problem that the conventional breather circuit cannot cope with the required increment/decrement of breather gas depending on the increment/decrement of fuel-supply rate.
As a technique for solving the problem, Japanese Unexamined Patent Publication (KOKAI) Gazette No. 8-216, 707, for instance, discloses an apparatus for prohibiting evaporating fuel gases from being emitted, apparatus which is provided with means for making an opening area variable. It also discloses to make the circulation volume of evaporating fuel gases variable depending on fuel-supply rates.
However, using the means for making an opening area variable, means which is disclosed in Japanese Unexamined Patent Publication (KOKAI) Gazette No. 8-216, 707, results in the following problem that the apparatus is susceptible to the limited on-board space. That is, in order to flow vapors in a large volume when the float valve (62) opens in FIG. 4 disclosed in the gazette, for instance, it is required to dispose a passage with a large cross-sectional area between the case (60) and the float valve (62). If such is the case, the size of the case (60) has enlarged so that the resulting apparatus suffers from the problem of limited on-board space.
Hence, Japanese Unexamined Patent Publication (KOKAI) Gazette No. 2006-2, 932 proposes a variable flow valve, which not only can precisely cope with the increment/decrement of required breather-gas flow resulting from the increment/decrement of fuel-supply rate but also can manage to offer a reduced on-board space. The variable flow valve comprises a housing, a valve element, and urging means. A first valve and a second valve are formed between the housing and the valve element. The variable flow valve copes with high-rate fuel supply and low-rate supply flexibly by means of controlling the balance between the opening/closing of the first valve and the opening/closing of the second valve.
As disclosed in Japanese Unexamined Patent Publication (KOKAI) Gazette No. 2006-2, 932, the variable flow valve has a valve element 100 as illustrated in FIG. 13. Specifically, the valve element 100 comprises a bottomed-tube-shaped cylinder 101, and a flange 102. The flange 102 protrudes radially outward from an outer peripheral surface of the cylinder 101. A spring 200, the urging means, urges the valve element 100 in such a direction that the valve element 100 goes toward the outlet opening.
During low-rate fuel supply shown in FIG. 13, gases within a fuel tank pass through the inside of the valve element 100. Then, the gases flow to the outlet opening through a clearance 301, which is formed between the valve element 100 and a housing 300.
On the other hand, during high-rate fuel supply, the gaseous pressure within the fuel tank increases, and the increasing pressure acts onto the valve element 100. Accordingly, the valve element 100 starts ascending. Then, as illustrated in FIG. 14, another clearance 302 arises between the lower base of the valve element 100's cylinder 101 and the housing 300 so that the gaseous pressure within the fuel tank acts onto the valve element 100's flange 102 as well. Consequently, the gaseous pressure pushes up the valve element 100 furthermore upward. The thus ascending valve element 100 throttles the opening area of the clearance 301. When the opening area of the clearance 301 is throttled, the pressure difference between the lower side under the valve element 100's flange 102 (i.e., the tank inner side) and the upper side above the valve element 100's flange 102 (i.e., the fuel-supply opening side) increases sharply because the atmospheric pressure acts onto the upper side above the valve element 100's flange 102. Thus, as illustrated in FIG. 15, the valve element 101 ascends instantaneously, and thereby enlarges the opening area of the clearance 302 immediately. As a result, the variable flow valve disclosed in Japanese Unexamined Patent Publication (KOKAI) Gazette No. 2006-2, 932 opens up.
Therefore, the variable flow valve disclosed in Japanese Unexamined Patent Publication (KOKAI) Gazette No. 2006-2, 932 is good in terms of the response to the changes of gaseous pressure. When the conventional variable flow valve is used in a breather circuit, it can flexibly cope with high-rate fuel supply and low-rate fuel supply. Moreover, since the first and second valves are formed between the valve element 100's flange 102 and the housing 300, it is possible to flow vapors in a great flow volume even when using the valve element 100 with small size. Therefore, the conventional variable flow valve can help engineers avoid the problem of limited on-board space.
However, the variable flow valve disclosed in Japanese Unexamined Patent Publication (KOKAI) Gazette No. 2006-2, 932, when the valve element 100 ascends to open the second valve, there occurs such a flow that fuel vapors swirl around the valve element 100's cylinder 101. Accordingly, the flow of fuel vapor is likely to be a turbulent flow. Consequently, the conventional variable flow valve might have such a drawback that it has exhibited a large ventilation pressure loss.
Moreover, Japanese Unexamined Patent Publication (KOKAI) Gazette No. 2004-100, 622 discloses a valve assembly as illustrated in FIG. 16. As shown in the drawing, the conventional valve assembly comprises a low-pressure opening valve 500, and a high-pressure opening valve 600. The low-pressure opening valve 500 and high-pressure opening valve 600 are disposed between a canister and the gaseous phase within a fuel tank. In the low-pressure opening valve 500, a ball 501 makes a valve body. The high-pressure opening valve 600 holds the low-pressure opening valve 500 therein. Upon automatically stopping fuel supply, the low-pressure opening valve 500 opens so that it is possible to decrease the pressure within the fuel tank. Note that Japanese Unexamined Patent Publication (KOKAI) Gazette No. 11-2, 348 discloses another one of such valve assemblies, which operate likewise.
However, these conventional valve assemblies might suffer from the following drawback. Namely, in order to secure a flow volume or in order to make the ventilation pressure resistance small, it is necessary to make the cross-sectional area of the flow passages when their valves are opened. As a result, the conventional valve assemblies have been large-sized so that they are disadvantageous in view of on-board space.